Scientists got a bunch of zebrafish addicted to opioids in an effort to better understand how to combat the drug epidemic, according to a new study.

Researchers are trying to come up with more effective treatment therapies that don’t involve replacing one opioid, such as heroin, with another like methadone — which can fix one addiction but saddle the patient with a new one.

“There is still a compelling need for therapies that work in different ways, not just by replacing one opioid with another,” Randal Peterson, dean of the College of Pharmacy at the University of Utah, told National Geographic.

The 2½-inch tropical fish are remarkably similar to humans and share about 70 percent of the same genes. They are also prolific breeders. This allows researchers to test new therapies quickly and on large populations. Their findings were published in the journal Behavioral Brain Research.

The research team set up a fish tank that had two platforms — one white and one yellow — and placed a sensor on the yellow one. When the fish swam over the sensor, the yellow platform released food and flashed a green light. The white platform did nothing.

After the fish figured out how the sensor worked, the food was replaced with Vicodin. Every time the fish swam over the yellow platform, the drug was released into the water. Researchers kept dumping and refilling the tank with fresh water to see if the fish would continue swimming over it.

And they did — a lot. The fish were inside the tank for 50 minutes a day, five days in a row, during which time many swam over the sensor up to 2,000 times during a single session.

During sessions without the drug, the fish — who had grown anxious and agitated — still swam up to the sensor around 200 times. When the researchers raised the platform so that it stood in shallow water — something zebrafish hate — the fish kept swimming up to the surface to try to get a hit.

“What’s new here is that this is a self-administration model where the fish have to perform an action to receive a drug, so that’s fundamentally different in terms of the way the brain responds to the drug,” Peterson said. “[This enables] us to measure motivation in drug-seeking in a more complete way.”

More than 33,000 Americans died from opioid addiction in 2015, and an estimated 2.6 million people are currently suffering from opioid addiction in the US.